3.13. The last thing we should talk about http://www.ck12.org
Until recently, all these pools of carbon were roughly in balance: all flows of carbon out of a pool (say, soils,
vegetation, or atmosphere) were balanced by equal flows into that pool. The flows into and out of the fossil fuel pool
were both negligible. Then humans started burning fossil fuels. This added two extraunbalancedflows, as shown
in figure 31.3.
The rate of fossil fuel burning was roughly 1 GtC/y in 1920, 2 GtC/y in 1955, and 8.4 GtC in 2006. (These figures
include a small contribution from cement production, which releasesCO 2 from limestone.)
How has this significant extra flow of carbon modified the picture shown in figure 31.2? Well, it’s not exactly
known. Figure 31.3 shows the key things thatareknown. Much of the extra 8.4 GtC per year that we’re putting into
the atmosphere stays in the atmosphere, raising the atmospheric concentration of carbon-dioxide. The atmosphere
equilibrates fairly rapidly with the surface waters of the oceans (this equilibration takes only five or ten years), and
there is a net flow ofCO 2 from the atmosphere into the surface waters of the oceans, amounting to 2 GtC per year.
(Recent research indicates this rate of carbon-uptake by the oceans may be reducing, however.) This unbalanced
flow into the surface waters causes ocean acidification, which is bad news for coral. Some extra carbon is moving
into vegetation and soil too, perhaps about 1.5 GtC per year, but these flows are less well measured. Because roughly
half of the carbon emissions are staying in the atmosphere, continued carbon pollution at a rate of 8.4 GtC per year
will continue to increaseCO 2 levels in the atmosphere, and in the surface waters.